const _keyStr = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/='

// Base64 编码
export function e_encodeBase64(input : string) {
    let output = ''
        let chr1,
            chr2,
            chr3,
            enc1,
            enc2,
            enc3,
            enc4
        let i = 0

    while (i < input.length) {
        chr1 = input.charCodeAt(i++)
        chr2 = input.charCodeAt(i++)
        chr3 = input.charCodeAt(i++)

        enc1 = chr1 >> 2
        enc2 = ((chr1 & 3) << 4) | (chr2 >> 4)
        enc3 = ((chr2 & 15) << 2) | (chr3 >> 6)
        enc4 = chr3 & 63

        if (isNaN(chr2)) {
            enc3 = enc4 = 64
        } else if (isNaN(chr3)) {
            enc4 = 64
        }

        output = output + _keyStr.charAt(enc1) + _keyStr.charAt(enc2) + _keyStr.charAt(enc3) + _keyStr.charAt(enc4)
    }
    return output
}

// Base64 解码
export function e_decodeBase64(input : string) {
    let output = ''
        let chr1,
            chr2,
            chr3
        let enc1,
            enc2,
            enc3,
            enc4
        let i = 0

    input = input.replace(/[^A-Za-z0-9\+\/\=]/g, '')

    while (i < input.length) {
        enc1 = _keyStr.indexOf(input.charAt(i++))
        enc2 = _keyStr.indexOf(input.charAt(i++))
        enc3 = _keyStr.indexOf(input.charAt(i++))
        enc4 = _keyStr.indexOf(input.charAt(i++))

        chr1 = (enc1 << 2) | (enc2 >> 4)
        chr2 = ((enc2 & 15) << 4) | (enc3 >> 2)
        chr3 = ((enc3 & 3) << 6) | enc4

        output += String.fromCharCode(chr1)

        if (enc3 !== 64) {
            output += String.fromCharCode(chr2)
        }
        if (enc4 !== 64) {
            output += String.fromCharCode(chr3)
        }
    }

    return output
}
